Electronic data processing equipment is sometimes employed to handle confidential or classified data which is to be kept secret and protected from unauthorized disclosure. For example, TEMPEST security requires the suppression of electromagnetic (EMI) or radio frequency (RFI) signals of predetermined characteristic or frequency emanating from the processing system which may be used to gain intelligence about the classified data being processed. Assuming that the processing system must be operational substantially 100 percent of the time, it will be appreciated that any equipment malfunction requiring trouble-shooting and repair, or even routine maintenance, pose a severe problem. The opening of a processor cabinet will destroy the TEMPEST or EMI integrity, and permit the classified data to be detected by unauthorized individuals.
In the past, high isolation requirements have been achieved by relay or transformer coupling, or by expensive fiber-optic connected infrared emitters and photodetectors, occupying large areas and powered by highly isolated power supplies. Moreover, as in the referenced patent, such previously used methods interfaced only two devices or circuits and were capable of operation at comparatively low speeds.
The isolator/switching assembly of the present invention meets the desired isolation objectives in a low cost, compact unit which permits common control by two processors, a MASTER and a BACKUP unit respectively, of several devices or ports at high data rates. The processor cabinets and the secured peripherals are electrically and mechanically independent of one another and are isolated to the extent that maintenance of any device or processor may be accomplished without turning down the system or compromising the TEMPEST integrity thereof.